Combustors are commonly used in industrial and commercial operations to ignite fuel to produce combustion gases having a high temperature and pressure. For example, an industrial gas turbine may include one or more combustors to generate power or thrust. A typical commercial gas turbine used to generate electrical power may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Ambient air may be supplied to the compressor, and rotating blades and stationary vanes in the compressor progressively impart kinetic energy to the working fluid (air) to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows through one or more nozzles in each combustor where the compressed working fluid mixes with fuel and ignites to generate combustion gases having a high temperature and pressure. The combustion gases expand in the turbine to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The fuel supplied to the combustor may be a liquid fuel, a gaseous fuel, or a combination of liquid and gaseous fuels. If the liquid and/or gaseous fuel is not evenly mixed with the compressed working fluid prior to combustion, localized hot spots may form in the combustor. The localized hot spots may increase the production of nitrous oxides in the fuel rich regions, while the fuel lean regions may increase the production of carbon monoxide and unburned hydrocarbons, all of which are undesirable exhaust emissions. In addition, the fuel rich regions may increase the chance for the flame in the combustor to flash back into the nozzles and/or become attached inside the nozzles which may damage the nozzles. Although flame flash back and flame holding may occur with any fuel, they occur more readily with high reactive fuels, such as hydrogen, that have a higher burning rate and a wider flammability range.
A variety of techniques exist to allow higher operating combustor temperatures while minimizing undesirable exhaust emissions, flash back, and flame holding. Many of these techniques seek to reduce localized hot spots to reduce the production of undesirable emissions and/or reduce low flow zones to prevent or reduce the occurrence of flash back or flame holding. For example, continuous improvements in nozzle designs result in more uniform mixing of the fuel and compressed working fluid prior to combustion to reduce or prevent localized hot spots from forming in the combustor. Alternately, or in addition, nozzles have been designed to ensure a minimum flow rate of fuel and/or compressed working fluid through the nozzle to cool the nozzle surfaces and/or prevent the combustor flame from flashing back into the nozzle. In still further embodiments, water may be added to the fuel to produce an emulsified fuel, and the nozzle may mix the emulsified fuel with the compressed working fluid prior to combustion to reduce the peak flame temperature, and thus nitrous oxide production, in the combustor. However, the emulsified fuel, if not adequately dispersed, may result in flame instability and/or increased undesirable exhaust emissions. Therefore, continued improvements in the combustor nozzle designs and methods for supplying fuel to the combustor would be useful to improve combustor efficiency, reduce undesirable emissions, and/or prevent flash back and flame holding events.